In general, motor vehicles and trucks of a known type are provided with a conventional air-conditioning system, i.e., a system of the type comprising a compressor, a condenser/electric-fan assembly, an expansion valve and an evaporator/electric-ventilator assembly, set cascaded to one another along a refrigerating circuit containing a coolant, for example R410A, and in which, in a way similar to what occurs in an automobile, the compressor is driven via a belt by the internal-combustion engine of the truck when said internal-combustion engine is running.
In this way, the air-conditioning system can be freely used in travelling conditions. However, when the truck is parked for a pause, to enable the driver to rest or have a sleep, it would be necessary to keep the engine running if the aim is to keep the air-conditioning system operating.
It is evident that the need to keep the engine of the truck running for the purpose indicated above represents a far from efficient use of the engine and moreover leads to early wearing-out of the latter, as well as high values of fuel consumption and of pollutant emissions.
With the purpose of overcoming these drawbacks, auxiliary air-conditioning systems have been proposed, designed to be connected to the primary air-conditioning system, i.e., the pre-existing one, of the truck and provided with an auxiliary air-conditioning unit comprising a small auxiliary internal-combustion engine, an auxiliary compressor, and an auxiliary condenser/electric-fan assembly. Said auxiliary unit is connected, by means of pipes and valves, in parallel with the corresponding air-conditioning unit of the primary system so as to be able to close a refrigerating circuit alternatively with the aforementioned expansion valve and with the aforementioned evaporator/electric-ventilator assembly of the primary system.
One such solution, albeit overcoming the drawbacks listed above, entails a costly and complex modification of the primary air-conditioning system.